how many times does the spark plug fire/revolution on a 2-stroke?

[breakdirt916]

for tach/hour meter on a 1997 CR80R

2 stroke: plug fires @ TDC, the piston goes down, then comes back up to TDC and fires again

so once per revolution?

[Rambunctous]

yup

[breakdirt916]

nice...it's setup that way from the company

blows my mind how rarely I see an hour meter on a 2-stroke...everyone says "it's got 1 hour on the new top end"

[Rambunctous]

nice...it's setup that way from the company

blows my mind how rarely I see an hour meter on a 2-stroke...everyone says "it's got 1 hour on the new top end"

The sparkplug in a two stroke fires exactly the same number of times as a 4 stroke that has a magneto if they are running at the same rpm's.

[Rambunctous]

A hour meter counts how long the engine has been running. It doesn't count the total number of revolutions. In would not know if it was idling for a hour or revving at 9000 RPM for a hour.

[Kurlon]

Many hour meters now double as tachs also.

[Dave603]

The sparkplug in a two stroke fires exactly the same number of times as a 4 stroke that has a magneto if they are running at the same rpm's.

I am confused... A magneto is a secondary form of electrical generation, why would it spark on both the powerstroke and the intake stroke?

[Kurlon]

I am confused... A magneto is a secondary form of electrical generation, why would it spark on both the powerstroke and the intake stroke?

The flywheel doesn't know if it's on a power stroke or not when it goes around. The system is setup so once each rotation of the flywheel energy for a spark is built up and then dumped at whatever crank position is correct. Because the flywheel runs at crank speed and not cam speed that means once per revolution.

[Dave603]

nice...it's setup that way from the company

blows my mind how rarely I see an hour meter on a 2-stroke...everyone says "it's got 1 hour on the new top end"

When you are riding a dirtbike without a gage cluster it is easier to know how many "hours" you've ridden rather than how many miles you've gone. Unless you carry a garmin.

- - - Updated - - -

The flywheel doesn't know if it's on a power stroke or not when it goes around. The system is setup so once each rotation of the flywheel energy for a spark is built up and then dumped at whatever crank position is correct. Because the flywheel runs at crank speed and not cam speed that means once per revolution.

Ok. I buy that. Thanks!

[Kurlon]

Ok. I buy that. Thanks!

If you ever hear the phrase 'wasted spark' this is what it means.

[slowkermit]

I learned something today!

[Rambunctous]

A car is different. The distributer runs off the camshaft. At half the revolutions of the crank. It doesn't do the "wasted spark. As a side note engines with timing chains need to have the timing check regularly because chains stretch. The crankshaft / camshaft position sensor will signal the computer to advance / retard the spark to make up the difference to some degree.

[breakdirt916]

When you are riding a dirtbike without a gage cluster it is easier to know how many "hours" you've ridden rather than how many miles you've gone. Unless you carry a garmin.

ya, I know that you count it by hours...I ride dirtbikes

what I have beef with, is that everyone is very optimistic about how many hours they're "estimating" to be on the top end when they're selling it...if it's been 10 hours or 100 hours, everyone says "it's got 2 hours on the top end"

if you really care about the maintenance of a dirtbike, why not get an hour meter?

I bought one for ~$10

[Dave603]

ya, I know that you count it by hours...I ride dirtbikes

what I have beef with, is that everyone is very optimistic about how many hours they're "estimating" to be on the top end when they're selling it...if it's been 10 hours or 100 hours, everyone says "it's got 2 hours on the top end"

if you really care about the maintenance of a dirtbike, why not get an hour meter?

I bought one for ~$10

Yeah it seems logical.. DO the new ones come with one? I mean either way though that still won't stop people from lying how many hours are on a rebuild.. unless your bike had a meter and you had a shop do it that recorded that on the printed receipt?

[RandyO]

A hour meter counts how long the engine has been running. It doesn't count the total number of revolutions. In would not know if it was idling for a hour or revving at 9000 RPM for a hour.

that's the way hour meters were on old tractors, the tach's were mechanical, and in the center like a speedo with an odometer, they has an hour meter, but in fact it was a revolution meter and what it actually displayed was hours at a specific rpm, if the engine was running slower, it would take more than an hour for one hour to roll over on the tach, or if it was running faster it would take less than an hour

[RandyO]

I always thought 4stroke thumpers like a briggs & stratton lawnmower engine had points and condensor, while the magneto has a pulse every revolution, the points are opened and closed by the cam and the spark plug only fires one every other revolution

[Kurlon]

I always thought 4stroke thumpers like a briggs & stratton lawnmower engine had points and condensor, while the magneto has a pulse every revolution, the points are opened and closed by the cam and the spark plug only fires one every other revolution

Depends on the bike, some ran the points off the crank, some off the cam. For simplicity's sake most went back to crank triggering when they went TCI/CDI as it eliminates the need for a seal and wiring from the head, you just piggyback the sensor wire in with the exciter wire from the stator cover.

[RandyO]

and then there's the old hit and miss engines

http://www.youtube.com/watch?v=TmZPFVpdHs4

[stoinkythepig]

I always thought 4stroke thumpers like a briggs & stratton lawnmower engine had points and condensor, while the magneto has a pulse every revolution, the points are opened and closed by the cam and the spark plug only fires one every other revolution

B&S motors run the points off the crank, so they fire on every revolution.

[breakdirt916]

I don't really care about a tachometer on a mini supermoto bike...

so I just set it up to only count the hours (no engine speed will display)

tick-tock